1. Technical Field
The present invention relates to a apparatus and to a method, for generating a multi-component compound, in particular for dental purposes.
2. Description of the Related Art
In general, known apparatuses for generating a multi-component compound for dental purposes operate by pressing its typically high viscous components out from exchangeable cartridges. These cartridges are arranged side-by-side, and they open into a static or dynamic mixer. An electric drive acts on plungers associated with the cartridges to advance them jointly for pressing out the components. In some apparatuses, the plungers are driven by motors that are not regulated or controlled at all. This leads to varying revolutions per minute and therefore to varying plunger velocities, which affects the mixing quality and application time. Within these apparatuses it is not possible to adapt the plunger velocity and mixer speed to the various paste characteristics with little expenditure.
There exist also other known apparatuses and methods, wherein the advance speed of the plungers is adjustable. It is generally desired that the plungers be advanced for positioning rapidly. When the plungers make contact with the components, the resistance and therefore the load for the drive increases. The advance speed should then be regulated to a lower constant value in order to ensure that the components are pressed out at a uniform speed.
Furthermore, it has been found that in many cases it is not sufficient to regulate the advance speed to a constant value. Instead it is also necessary to select the suitable advance speed due to different types of components, which have very different properties, e.g. viscosities, or which require particular speeds due to processing factors. Depending on the properties of the components, there is an optimum advance and a good and reproducible result of the work.
EP 1 101 538 A2 and U.S. Pat No. 6,371,336 B1 each discloses an electrically operated dispensing appliance. This known appliance comprises a gear motor which is connected to the main shaft by a first gear and a first shifting sleeve in order to operate the advance and the relieving stroke under high loads. For the operation at smaller loads, i.e. fast retraction and fast forward feed, it is connected to the main shaft by a second gear, a driving shaft, and a second shifting sleeve. An electromagnet is connected to said two shifting sleeves in such a manner that one or the other shifting sleeve is selectively connectable to the main shaft.
EP 0 956 908 A1 and U.S. Pat. No. 6,168,052 B1 each discloses an electrically driven dispensing appliance. This known appliance comprises an electric drive that acts via drive screws on thrust plates for dispensing material from cartridges. The different forces acting upon the two drive screws are supported by rolling friction on low friction bearings so that no tilting forces on the slide are generated. The electric drive comprises a first gear motor for a drive under high load during advance and relief, and a second motor for the drive under lower load during the retracting and fast advance motions.
EP 0 492 413 A1 and U.S. Pat. No. 5,286,105 each discloses an apparatus for mixing and applying two-component materials. This known apparatus comprises two pistons which can be displaced and driven forward together by an electric motor via a magnetic coupling in the cartridges. The pistons can be drawn back manually. and inserted again via a manual wheel when the motor is switched off and the magnetic coupling moved out. In this application the motor drive is only designed for a slow advance of the pistons, wherein the changing of the cartridges is due to the manual extension and retraction of the pistons.
EP 1 010 401 A1 and U.S. Pat. No. 6,315,164 B1 each discloses a method and apparatus for generating a multi-component compound, in particular for dental purposes, by pressing its components out from exchangeable cartridges into a mixer. In this known apparatus, the advance speed is constantly kept at a predetermined value, to ensure that the mixing quality is not adversely affected by the advance speed differing depending on viscosity and friction ratios. This is preferably achieved by means of a unit which is assigned to the drive motor. This unit can also be used for driving the motor, depending on the load, either at a low speed assigned to the normal advance, or at a higher speed assigned to the return movement.
EP 1 279 379 A1 and US 2003/0 022 128 A1 each discloses an apparatus for generating a multi-component compound, in particular for dental purposes, by pressing out and mixing its components from cartridges which open into a mixer. In this known apparatus the advance speed of the electric motor is regulated by the pressing-out behavior of the components, which pressing-out behavior can be determined by sensors. Preferably, the electric motor is a DC motor.
In view of the above, to ensure a desired driving, i.e. advancing and returning speed of the plungers, DC motors are used in general. The torque characteristic of DC motors or shaded pole motors is the opposite of what is needed for the application, because they offer low torque at the low speed drive modus, whereas high torque is needed for pressing out the components. Furthermore, at very low speeds, of about 1 to 10 revolutions per minute, the operation of a conventional DC motor actually breaks down.
These drawbacks are often countered by complex gearboxes, manual interactions of users, a plurality of motors, or a plurality of driving units assigned to the drive motor and linked with additional sensors.